(a) Field of the Invention
The present invention relates to a method for manufacturing a photoreceptor drum for use in a copying machine, a facsimile machine, a printer, or a like apparatus, and more particularly to a photoreceptor (hereinafter referred to as a "porous photoreceptor") having a surface formed as a porous layer, in which a large number of equally spaced fine pores are formed, and to a method for manufacturing the porous photoreceptor. The present invention also relates to a porous photoreceptor manufactured by such a method.
(b) Description of the Related Art
Conventionally, an electrophotographic process has been widely used as an image formation technology employed by copying machines, facsimile machines, printers, and like apparatus. The Carlson process (xerography) is a typical electrophotographic process, which includes six steps for printing, including electrification, exposure, development, transfer, fixing, and cleaning. Since a dedicated unit must be installed for each step, the entire system unavoidably becomes large-scaled.
The inventors have disclosed an image recording method in Patent Publication No. JP-A-1997-204092 corresponding to U.S. Pat. No. 5,815,774, as a simplified electrophotographic process to replace the Carlson process. The disclosed method employs a porous photoreceptor composed of a photoreceptor and a porous insulation layer formed on the surface of the photoreceptor. An electrode is formed on the upper surface of the porous insulation layer. Conductive coloring particles are filled into pores formed on the thus-configured porous photoreceptor. The porous photoreceptor is exposed to light corresponding to print information, thereby selectively causing the coloring particles to move in the air toward an counter electrode and be thus transferred onto recording sheet located on the near side of the counter electrode. Since this method completes printing in three steps--a coloring particles filling step, an exposure and transfer step, and a fixing step, the associated equipment can be reduced in size.
The above porous photoreceptor may be manufactured by the steps of forming pores in a sheet of the porous insulation layer by laser or drilling, and closely attaching the sheet onto the drum-shaped photoreceptor. However, a seam is formed between the abutting ends of the sheet and becomes apparent in the form of an image defect, thus impairing image quality. In the case of using a laser for forming the pores, the pores can be finely finished, and thus a high degree of image quality is obtained; however, mass productivity is rather poor with a resultant increase in cost of manufacture. In the case of forming the pores by mechanical means, such as by drilling, drilling must be repeated a tremendously large number of times. For example, when a porous layer having pores formed therein at a resolution of 200 dpi is to be formed on a cylindrical photoconductive layer having a length of 210 mm, which is the length of size A4 sheet, and a diameter of 30 mm, the number of pores to be formed becomes at least one million. Since only one pore can be formed by a single operation of drilling, drilling must be repeated at least one million times, which is not practical.
To cope with the above problems, in Japanese Patent Application No. 1997-317245, we have proposed a method for forming a porous layer in which a photo-setting liquid resin is used.
The method includes the steps of applying the photo-setting liquid resin onto a photoconductive layer; causing the applied photo-setting liquid resin to be selectively set so as to establish contrast of set portions and unset portions in correspondence with desired patterns of pores; and eliminating the unset portions to thereby form a porous layer. However, the photo-setting liquid resin encounters difficulty in forming the porous layer to a uniform thickness. In addition, since the photo-setting liquid resin usually has high viscosity, the resin involves difficulty in handling during application thereof.
In the printing method described in U.S. Pat. No. 5,815,774, image density is determined by the number of coloring particles contained in each of the larger number of pores. In order to contain a certain number of coloring particles in each pore, the diameter of the pore must assume at least a certain minimum value, or the depth of the pore must assume at least a certain minimum value, i.e., the thickness of the porous layer must assume at least a certain minimum value. The diameter of the pore is preferably decreased in order to improve resolution for printing a high-quality image. Accordingly, in order to obtain a certain image density, the depth of the pore, i.e., the thickness of the porous layer, is made to assume at least a certain minimum value. However, in the case of formation of a large number of through-pores in a photo-setting resin layer, with the increase in the thickness of the photo-setting resin layer, elimination of unset portions becomes more difficult, i.e., formation of pores becomes more difficult.
As described above, formation of the porous layer is a key technology for the printing method described in U.S. Pat. No. 5,815,774. However, although a laser can process the porous layer to a high degree of fineness with resultant high image quality, employment of a laser has a drawback of high cost due to poor mass productivity. Formation of pores by mechanical means, such as by drilling, encounters difficulty in processing the porous layer to a high degree of fineness and is thus unsuited for formation of the porous layer. In the case of the method disclosed in Japanese Patent Application No. 1997-317245, formation of the porous layer to a uniform thickness is difficult because of employment of a liquid resin. The liquid resin involves difficulty in handling during application thereof and fails to meet a demand that the porous layer be formed to at least a certain minimum thickness in order to obtain high image density.